Doughnut frying machines are known. Typical examples are shown in U.S. Pat. Nos. 3,945,785 and 4,346,649. In these types of doughnut frying machines or fryers, the dough is stored in a hopper and extruded out through a cylinder or cylinders forming a cutter in the bottom of the hopper by reciprocating piston mechanisms. An upper piston pushes the dough into and out of the cylinder, whereas a lower piston on operation creates a partial vacuum to allow the air pressure to move the dough into the cylinder. The lower piston also can be retracted to serve as a cutter to cut the extruded dough from the dough remaining in the cylinder by engaging the lower piston against the bottom cutting edge of the cylinder. The doughnut that forms is the typical toroidal shape and falls by gravity into a frying tank, between the flights of a moving conveyor, or into an open kettle.
As long as the doughnuts or other edible products are reasonably large in size, the weight of the product is sufficient to produce a clean and quick separation from the cutting edge of the hopper cylinder. During the extrusion of the dough, particularly non-yeast dough as is used in making doughnuts, components of the dough, such as gluten or other sticky substances, will build up and form a film on the cutting edge of the cylinder and the cutting piston. With heavier doughnuts, the weight of the doughnut is sufficient to still provide a reasonably clean and quick separation from the cutting edge of the cylinder. With lighter weight doughnuts, such as mini-doughnuts, which are frequently formed in multiple cylinders in a single hopper, the gluten attached to the cutting surfaces adheres to the extruded formed doughnut dough, leaving strings of dough attached to the cutting surfaces when the doughnut finally falls free. More importantly, however, the adhesion of the dough to the gluten-coated cutting surfaces occasionally causes the doughnut to adhere and fall only after a nonuniform time delay such that, when the doughnut does fall, it will not fall between the flights on the conveyor but may land on a conveyor flight, damaging the product and causing the need for more frequent cleaning of the equipment. Also, if the doughnut sticks at one end it can topple onto its edge while falling into the cooking oil and be distorted in shape.
An apparatus and a method for preventing lightweight doughnuts from adhering to the cutting surfaces of a doughnut frying machine is disclosed in U.S. Pat. No. 5,100,685 the '685 patent), which is incorporated herein by reference. The apparatus and method disclosed in the '685 patent prevents sticky, glutinous substances from building up on the cutting surfaces by providing edible oil to the cutting surfaces. As a result, the lightweight doughnuts do not adhere to the cutting surfaces.
The apparatus and method disclosed in the '685 patent works well to prevent glutinous substance build-up and consequent doughnut adhesion. The '685 patent covers any form of edible release oil. One form of release oil is the oil used to fry the doughnuts.